﻿<p>The <em>IfcBoxedHalfSpace</em> is used (as its supertype <em>IfcHalfSpaceSolid</em>) only within Boolean operations.
It divides the domain into exactly two subsets, where the domain in question is that of the attribute
<em>Enclosure</em>.</p>
<p>The purpose of the attribute <em>Enclosure</em> is to provide a search box for the other operand in the Boolean
operation. It shall be sufficiently large to fully enclose the resulting solid after the Boolean operation with the
half space. It however does not alter the final result. The result of the Boolean operation would be the same, as if
executed by the supertype <em>IfcHalfSpaceSolid</em>. See Figure 3 below.</p>
<table summary="boxed half space">
<tr>
<td><img src="../../../figures/ifcboxedhalfspace_01.png" alt="correct use of enclosure" border="0"></td>
</tr>
<tr>
<td>
<p class="figure">Figure 3 &mdash; Boxed half space operands</p>
</td>
</tr>
</table>
<p>The <em>IfcBoundingBox</em> that provides the enclosure is given for the
convenience of the receiving application to enable the use of size box comparison for efficiency (for example, to check
first whether size boxes intersect, if not no calculations has to be done to check whether the solids of the entities
intersect).</p>
<table summary="boxed half space">
<tr>
<td width="600" valign="top" align="left"><img src="../../../figures/ifcboxedhalfspace-layout1.png" border="0" height="480"
width="600" alt="boxed half space"></td>
<td>The <em>Enclosure</em> therefore helps to prevent dealing with infinite-size related issues. The enclosure box is
positioned within the object coordinate system, established by the <em>ObjectPlacement</em> of the element represented
(for example, by <em>IfcLocalPlacement</em>). Figure 4 shows the <em>Enclosure</em> box being sufficiently large to
fully enclose the Boolean result.</td>
</tr>
<tr>
<td>
<p class="figure">Figure 4 &mdash; Boxed half space geometry</p>
</td>
<td>&nbsp;</td>
</tr>
</table>
<p>&nbsp;</p>
<blockquote class="extDef">NOTE&nbsp; Definition according to ISO/CD 10303-42:1992<br>
This entity is a subtype of the half space solid which is trimmed by a surrounding rectangular box. The box has its
edges parallel to the coordinate axes of the geometric coordinate system.<br>
The purpose of the box is to facilitate CSG computations by producing a solid of finite size.</blockquote>
<blockquote class="note">NOTE&nbsp; Entity adapted from <strong>boxed_half_space</strong> defined in ISO
10303-42.</blockquote>
<blockquote class="history">HISTORY&nbsp; New entity in IFC1.5.1</blockquote>
<blockquote class="change-ifc2x4">IFC4 CHANGE&nbsp; Usage correct, position coordinate system for <em>Enclosure</em>
is the object coordinate system.</blockquote>

